title: Systems factors in obstetric care: the role of daily obstetric volume.
abstract: OBJECTIVE
  To evaluate whether relatively high-volume days are associated with measures of obstetric care in California hospitals.
  
  
  METHODS
  This is a population-based retrospective cohort study of linked data from birth certificates and antepartum and postpartum hospital discharge records for California births in 2006. Birth asphyxia and nulliparous, term, singleton, vertex cesarean delivery rates were analyzed as markers of quality of obstetric care. Rates were compared between hospital-specific relatively high-volume days (days when the number of births exceeded the 75th percentile of daily volume for that hospital) and low-volume or average-volume days. Analyses were stratified by weekend and weekday and overall hospital obstetric volume. Multivariable logistic regression was used to control for confounders.
  
  
  RESULTS
  On weekends, relatively high-volume days were significantly associated with an elevated risk of asphyxia (27 out of 10,000 compared with 17 out of 10,000; P=.013), whereas no association was present on weekdays (13 out of 10,000 on high-volume days and 15 out of 10,000 on low-volume or average-volume days; P=.182). The cesarean delivery rate among the nulliparous, term, singleton, vertex population was significantly lower on high-volume weekend days (22.0% compared with 23.6% on low-volume or average-volume weekend days; P=.009), whereas no association was present on weekdays (27.1% on high-volume days and 27.6% on low-volume or average-volume days; P=.092).
  
  
  CONCLUSIONS
  Delivery on relatively high-volume weekend days is a risk factor for birth asphyxia in California. High-volume weekend days also are associated with a lower rate of cesarean delivery in nulliparous women with singleton, vertex presentation pregnancies at term.
  
  
  METHODS
  : II.
authors.affiliation: Departments of Obstetrics and Gynecology, Medical Informatics and Clinical Epidemiology, and Emergency Medicine, and the Center for Health Systems Effectiveness, Oregon Health and Science University, Portland, Oregon; and the Department of Obstetrics, Gynecology, and Reproductive Sciences, University of California, San Francisco, California.
authors.forename: Jonathan M
authors.initials: JM
authors.lastname: Snowden
authors.forename: Blair G
authors.initials: BG
authors.lastname: Darney
authors.forename: Yvonne W
authors.initials: YW
authors.lastname: Cheng
authors.forename: K John
authors.initials: KJ
authors.lastname: McConnell
authors.forename: Aaron B
authors.initials: AB
authors.lastname: Caughey
mesh_terms: D001238:Asphyxia Neonatorum / Q000453:epidemiology*; D002140:California / Q000453:epidemiology; D002585:Cesarean Section / Q000706:statistics & numerical data*; D005260:Female; D006801:Humans; D007231:Infant, Newborn; D016015:Logistic Models; D009774:Obstetrics; D011247:Pregnancy; D012189:Retrospective Studies; D000078329:Workforce